Like I said, check with your friendly Oracle salesman. Not speaking for the company, but Oracle seems pretty un-up-tight about people using their software without paying for it, though I assume they would get pretty uptight if you started selling the results of using their product without paying for licensing.
Their strategy has worked as I've spent (tens of) millions on Oracle over the years.
Also, if all you want is an ERD, or more accurately a server model, you can use either Access or reverse engineer it into Erwin, Rational Rose, Oracle Designer, etc. I would only use JDeveloper if you absolutely must have a UML diagram.